Automatic braking system

ABSTRACT

A brake control system for automatically providing a smooth, comfortable brake pressure application rate for achieving the desired deceleration level and for maintaining this level. The system consists essentially of a closed looped modulator which controls the brake valve. The modulator is responsive to a brakeapply signal to produce the desired deceleration rate. The system is also responsive to a brake-remove signal to produce smooth and comfortable removal of the brake application and the system is capable of being instantly overridden to return full braking control to the vehicle operator.

United States Patent Booher 1 1 Jan. 16, 1973 [54] AUTOMATIC BRAKINGSYSTEM FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Harold R. Booher,Youngstown, 1,956,398 5/1970 Germany .303/21 P Ohio PrimaryExaminerTrygve M. Blix [73] Asslgnee' E coodAyiar & Rubber AssistantExaminerStephen G. Kunin ompany Att0rneyF. W. Brunner, P. E. Millikenand Oldham [22] Filed: Sept. 30, 1970 and Oldham [21] Appl. No.: 76,904

[57] ABSTRACT US. Cl. P, l 1, A brake cgntrol ystem for automatically po iding a [51] Int. Cl. ..B60t 8/12 h, f able brake pressure applicationrate [58] Field O Se8 'C 88/l for achieving the desired decelerationlevel and for 303/21; 324/162; 340/262 maintaining this level. Thesystem consists essentially of a closed looped modulator which controlsthe brake 56 References Cit d valve. The modulator is responsive to abrake-apply signal to produce the desired deceleration rate. The UNITEDSTATES PATENT system is also responsive to a brake-remove signal to 3537 758 11/1970 Buhler et al 303/2 BE produce smooth and comfortableremoval of the 3494671 2/1970 slavin et 303/2 P brake application andthe system is capable of being 3520575 7/1970 Steigerwald' 3 BEinstantly overridden to return full braking control to 3,554,6l2 1 1971Harned ..303 21 BE the vehcle Operator- 3,275,384 9/1966 Hirzel....3'.)3/2l CG l0 Claims 3 Drawing Figures 3,017,!45 1/1962 Yarber.....303/2l P 3,556,6l0 l/l97l Leiber ..303/2l P 34a FEMOVE\ 7 e 7 32 (1AUTOMATIC TO BYPASS APPLY K WHEEL SPEED T BRAKE VALVE 8 11 35 32 9 FOOT2 PEDAL MODULATOR -26 -38 l4 *ZSVDC E 18 207 I0 I TRANSDUCER CONVERTER-22 DETECTOR VALVE 2 n: v v 1- 1 v a 4 e LOCKED WHEEL LOCKED WHEELAMPLIFIER ARMING DETECTOR -25 LANDE L 4o SQUAT 33 SWITCH i COMMUTATIONTO OTHER AUTO BRAKE CIRCUITS PATENTEDJAH I 6 Ian, 3.71 1. 163

3441 m FEMOVE E 307 I AUTOMATIC 32a T0 ZYPASS APPLY WHEEL SPEED VALVE III 32 g BAL- '"MODULATOR -26 -3 2.. I4 +zevoc 7 IO E l8 7 h TRANSDUCERCONVERTER DETECTOR 22; VALVE V 2 v I E V I, r I g LOCKED WHEEL LOCKEDWHEEL AMPLIFIER id ARMING DETECTOR -25 LANDE L28 29) 4o COMMUTATION ToSQUAT AIR SWITCH FROM CONVERTE Cl 5% (\ysEc) |AUTO-BRAKE I oIDECELERATION I=I=s OTHER AUTO BRAKECIRCUITS TouTPuT INVENTOR HAROLD R.BOOHER BYZ I I ATTORNEYS AUTOMATIC BRAKING SYSTEM This invention relatesto a brake controlling circuit which controls the brakes to provide asmooth and comfortable brake pressure application rate to achieve adesired deceleration level and to maintain that level.

It is desirable that the braking rate of a passenger vehicle be smoothand comfortable, particularly in commercial passenger aircraft wherepassenger comfort and safety is an important factor. It is alsodesirable that the braking action of the vehicle be consistent so that apredictable stopping distance be obtained. While normally the brakingrate is directly controlled by the vehicle operator, subject toanti-skid control circuits, a more uniform and predictable braking ratecan be achieved by means of an automatic circuit. Any brake controlsystem must be capable of being overridden by the vehicle operator whenthe situation requires.

It is the primary object of the present invention to provide a brakecontrol circuit which is capable of controlling the brakes so as toprovide a smooth and comfortable deceleration of the vehicle. It is alsothe object of the invention to provide a brake control circuit whichprovides consistent braking action to maintain a predictable stoppingdistance. Another object of the invention is to provide a brake controlcircuit which may be overridden by the vehicle operator to returnbraking control to him depending upon the requirements of the situation.Another object of the invention is the provision of a brake controlsystem which is capable of smoothly and comfortably releasing thebraking action of the vehicle upon command by the vehicle operator.

As will be pointed out more fully below, the present invention achievesthese objectives by providing a brake control system which includes aclosed loop modulator to smoothly bring the braking action to a desireddeceleration level and to maintain the action at that level.

The above and other objects and advantages of the invention will becomeapparent upon consideration of the following specification and theaccompanying drawing wherein there is shown a preferred embodiment ofthe invention.

In the drawing:

FIG. 1 is a block diagram of a complete brake control system employingthe automatic brake controlling circuit of the present invention;

FIG. 2 is a schematic showing of a preferred embodiment of the specificautomatic brake control circuitry; and

FIG. 3 is a graph showing the desired operating curve for a vehiclebraking system.

As shown in FIG. 1, the brake control system includes a valve whichcontrols the application of pressure to the brake 12 associated with avehicle wheel 14. An exciter ring 16 is mounted for rotation with thewheel 14. Associated with the exciter ring 16 is a transducer 18 locatedat the end of the axle and this combination constitutes a wheel-speedsensor. The electrical pulses generated by the transducer 18 are sent toa converter which produces a DC. voltage directly proportional to thewheel speed. The wheel speed dependent signal from the converter 20 issupplied to a skid detector circuit 22 which sends a control signal toamplifier 25. The signal from converter 20 is sent to a modulator 26.The signal is also supplied to a locked wheel arming circuit 28 and alocked wheel detecting circuit 29 which also controls the amplifier 25.The output signal of the amplifier 25 controls the operation of thevalve 10. The control system described above may be of the typedescribed in application Ser. No. 593,150, abandoned in favor ofcontinuation-inpart application, Ser. No. 871,512, filed Oct. 27, 1969,now U.S. Pat. No. 3,574,426 and operates to reduce brake pressure in theevent of a sudden decrease in wheel speed which occurs during a skid andto smoothly reapply brake pressure thereafter.

The automatic brake control feature of the present invention is achievedby a circuit 30 which produces an additional control signal to theamplifier 25. The brake control circuit is responsive to vehicleoperator initiated brake APPLY and brake REMOVE signals and to the wheelspeed dependent voltage signal from the converter 20. Upon receipt of abrake APPLY signal in conductor 32 the automatic brake circuit producesa signal in the conductor 38 to the valve amplifier circuit 25 Thissignal causes the brake valve 10 to be operated so as to apply thebrakes to smoothly achieve a comfortable deceleration rate and tomaintain the rate once achieved.

The automatic brake control circuit 30 is shown in detail in FIG. 2. Thecircuit consists essentially of the following component sections:

1. A closed loop pressure control modulator indicated as a whole bydotted block 42 and consisting of an integrating amplifier A3, resistorR6, capacitor C2, and zener diode VR4.

2. A deceleration comparator section indicated generally by dotted block44 which senses any deceleration error and provides an input to thepressure control modulator section 42 to effect a smooth and steadychange in brake torque.

3. A gate section indicated generally by dotted block 48 which iscontrolled by the apply/remove logic section 46 and either passes orprevents passage of the control signal from the modulator section 42 tothe amplifier 25 controlling the valve 10.

4. An automatic brake control logic section indicated generally bydotted block 46 which serves to control the APPLY and REMOVE signals tothe gate 48.

5. A deceleration detector section indicated by dotted block 31 whichdetects deceleration rate from the signal received from converter 20.

The automatic braking mode is selected by the pilot or vehicle operatorprior to landing by closing the arming switch 32a associated with line32. This arms the automatic brake controlled logic section 46 whichsupplies APPLY and REMOVE signals over lines 32 and 34 at the propertime. Also, it may energize a solenoid operated valve (not shown) whichbypasses the pilot operated power brake metering valve (not shown) so asto apply hydraulic system pressure to the inlet of the anti-skid valve10. These valve relationships are well known and standard in theanti-skid field. In this manner, the brake pressure is controlled solelyby the anti-skid valve 10 which receives commands through amplifier 25from the skid detector 22 and automatic brake circuit 30.

The automatic brake control logic section 46 senses aircraft touch-downby monitoring the position of the deceleration level is attained. Theautomatic control circuit 30 maintains this level until (1) the aircraftis stopped (2) a remove signal is received from the automatic brakecontrol logic 46 or (3) the pilot assumes control by depressing hisbrake peddle 35 which acts through the logic section 46.

If prior to a complete stop, the pilot chooses to taxi, he can close theremove switch 34a which sends a remove signal over line 34 to theautomatic brake circuit 30. Upon receipt of the remove signal, thecircuit 30 commands the anti-skid control valve to remove brake pressureat a smooth, even rate.

If, during an automatic stop, the pilot finds it necessary to assumecontrol of the braking effort, he can do so merely by depressing thebrake pedal 35. This opens the brake pedal interlock switch 37 causingthe automatic logic section 46 to terminate the APPLY signal. Loss ofthe APPLY signal causes immediate removal of the automatic brake controlsignal to the anti-skid valve 10. At the same time the normal hydraulicbraking system of the aircraft is actuated.

FIG. 3 illustrates in graphic form the normal braking deceleration infeet per second squared as related to valve volts per second, with thisbeing indicated by the curve 100 in solid line. The curve achieved bythe automatic brake section 30 will follow the dotted line graph 102.

The essence of the automatic brake circuit as depicted by the graph ofFIG. 3 is to maintain a steady deceleration rate of about 10 feet persecond squared, or any predetermined rate desired, unless prohibited bypoor runway conditions. Normally, the circuit of sections 42 and 44described more fully hereinafter will maintain that decelerationintersected by the vertical portion of curve 102 by causing the valvevoltage to change in either a positive or negative direction at the rateindicated by the horizontal sections of curve 102. This results in arate of brake pressure change (psi/sec) in the direction necessary tomaintain deceleration at the valve intersected on the abscissa by thevertical portion of curve 102. The maximum rates of valve voltage changeare 3 v/sec and +7 v/sec. These limits are arbitrary however, dependingon the valve electrical characteristics and the physical requirementsand limitation of the structure.

The predetermined deceleration rate of 10 feet per second squared ismaintained by the interaction of sections 31, 42, and 44. The electricalsignal received from A1 is the deceleration rate of wheel 14. Thissignal applied through R2 to the negative input of A2. The predeterminedoperating level of A2 is controlled by a predetermined input referencevoltage level to the positive terminal of AZ. This reference voltagelevel is set by the voltage divider network R4 and R5. A2 is anamplifier that produces an output at all times of either positive ornegative VDC depending on the relation of the input voltage from A1 asit falls above or below the reference voltage level. When below thereference level, a +l5 VDC signal is sent to A3 and when above thereference level a -l 5 VDC signal is sent to A3.

The integrator 42 generates a correction signal to maintain the desired10 ft/sec deceleration rate. The signal is built up or down at a ratedetermined by the electrical characteristics of resistors R6 and R6aacting in combination with capacitor C2. The rate is that indicated bythe horizontal sections of curve 102, ie, 7 v/sec up and 3 v/sec down.R6 in combination with diode CRScontrols the down rate of 3 volts persecond valve actuation energy for the example described, while R6a incombination with CR6 sets the up rate of +7 volts per second valveactuation energy. Valve voltage cannot rise above 10 VDC nor fall below0 VDC. Q3 acts as a series switch that applies the output of A3 toamplifier 25 via conductor 38 only when an APPLY signal is received fromlogic section 46. VR4 acts to limit the maximum output from A3 bybreaking down at a predetermined voltage. Hence, it is seen how thegraph of FIG. 3 is attained as the deceleration rate of IO ft.lseclimits up and down vertical portion of the graph to seek the propervoltage output to the valve 10.

SPECIFIC CIRCUIT DESCRIPTION The deceleration detector 31 detects theinstantaneous deceleration of the wheel so as to produce a DC level atits output that is proportional to the deceleration. This isaccomplished by differentiating the wheel speed. Cl R1, and Al form aclassic differentiator with the ratio of CI to R1 controlling the gainand with VR3 limiting the maximum output swing to prevent amplifier Alfrom saturating. The deceleration information from the decelerationdetector 31 is then sent to the deceleration comparator section 44formed by amplifier A2 and resistors R2 through R5. The decelerationcomparator section 44 compares the wheel deceleration with a presetreference deceleration and decides whether the wheel deceleration is toohigh or too low. If it is too high, the output of A2 switches to its lowstate. R4 and R5 form a voltage divider to provide the referencedeceleration signal.

The output of the deceleration comparator section 44 is applied to theinput of the pressure control modulator section 42. The modulatorintegrates the signal received from the deceleration comparator circuit44 so as to provide steadily increasing or decreasing control signals atits output that, when applied to the antiskid pressure control valve,will produce a smooth and steady change in brake torque in the directionto eliminate the deceleration error being sensed by the decelerationcomparator section 44.

The gate section 48 formed by 03 through Q5, CR4, and R7 through R9 actsas a series switch at the output of the pressure control modulatorsection 42. It is controlled by the apply/remove logic section 46 and iseither on or off, that is it either passes or prevents passage of thepressure control signal from the modulator section 42 to the valveamplifier 10 through the conductor 38. Q3 and R7 form the actual switchand are controlled by Q4 and Q5. When neither an APPLY nor a REMOVEsignal are present, O4 is held in conduction by R8 and CR4 andeffectively shorts to ground the base drive for Q3 thus holding switchQ3 in an open or off position. Also at this time, O2 is held inconduction through CR2 and R1 1 and provides plus 15 VDC bias, (throughR3) to the deceleration comparator section 44. The effect of the bias isto hold A2 at a low state despite the deceleration voltage appearing onR2. When A2 is in a low state the modulator section 42 is held at itszero brake pressure level until the bias voltage disappears. This occurswhen the APPLY signal activates logic section 46. For this to happen,apply switch 32a must be closed and the squat switch 33 must be inlanded position. The signal in conductor 32 blocks conduction of Q2which removes the bias voltage from the deceleration comparator section44 and permits it and the modulator section 42 to function normally. Thesignal in conductor 32 also causes Q5 to conduct which shuts down Q4 soas to permit Q3 to switch to a closed or on state thus connecting theoutputs of the modulator section 42 to the valve amplifier circuit 25through the conductor 38.

The result of the above sequence is to fully dump brake pressure at theinstant of airplane touchdown and to immediately begin reapplyingpressure at a smooth and steady rate. Pressure increases until the wheeldeceleration, as sensed through the deceleration detector 31, exceedsthe reference deceleration as determined by R4 and R5.

When a REMOVE signal appears in conductor 34, assuming that the APPLYsignal is present in the conductor 32, Q1 is biased on and shorts toground the portion of the APPLY signal that has blocked conduction of Q2and thus causes the bias signal to reappear in the comparator section44. With the bias signal present, the deceleration comparator section 44is held in its low state thus producing a command to the controlmodulator section 42 to reduce brake pressure to zero at a smooth andsteady rate.

If at any time the APPLY signal is removed from the conductor 32, evenif the REMOVE signal is present in the conductor 34, Q5 and Q4immediately switch Q3 to the open or off state removing the outputsignal of the pressure control modulator 42 from the valve amplifier 25so as to return full braking control to the operator and the normalanti-skid circuits.

Preferably, the automatic brake control system of FIG. 2 is connected toprovide simultaneous control of two wheels paired symmetrically oppositeeach other by connecting the valve amplifier 25 of each wheel to theoutput conductor 38 of the automatic brake control system.

Identical circuits control other wheels similarly paired. In order toprevent system lock out ie., one pair of wheels doing all of the workwhile the other pair coast, the automatic brake control circuits areinterconnected through R51 and conductor 40.

While in accordance with the Patent Statutes only one preferredembodiment of the invention has been described, it will be understoodthat the invention is not so limited and that reference should be had tothe appended claims in determining the scope of the invention.

What is claimed is:

l. A brake control system for use on a moving vehicle having at leastone rotatable wheel, brake means for the wheel, means to represent wheelrotation as a voltage, and valve means responsive to an electricalsignal for controllably actuating the brake means, comprising:

an integrating amplifier for supplying the electrical signal to thevalve means;

a first circuit means supplying a static reference signal to theamplifier;

a second circuit means responding to the means to represent wheelrotation as a voltage and supplying a wheel deceleration signalrepresentative of the instantaneous rotation of the wheel to the firstcircuit means to produce the static reference signal therefrom forcontrol of the integrating amplifier and the valve means;

skid detector circuit means supplying a signal indicative of skidconditions of the wheel to the valve to override the control outputsignal; and

a first logic circuit which, in response to a first external commandsignal, controls the ability of the wheel deceleration signal to effectthe output of the first circuit means.

2. The brake control system according to claim 1 which further includesa second logic circuit, responsive to the first external command signal,operative to supply the output of the integrating amplifier to the valvemeans only when the first external command signal is present.

3. The brake control system according to claim 2 wherein the first logiccircuit, in response to a second external command signal, controls the"ability of the wheel deceleration signal to affect the output of thefirst circuit means when the first external command signal is present.

4. The brake control system according to claim 1 wherein the integrationamplifier is such that the output thereof changes with respect to timeat two separate and distinct rates depending upon the relative polaritybetween the static reference signal and a predetermined reference.

5. A brake control circuit for a rotating wheel which comprises:

a brake for the wheel;

wheel speed detector means to sense and indicate instantaneous wheelspeed as an electrical signal;

a skid detector actuated by the electrical signal from the wheel speeddetector means so as to produce a first brake control signal; and

means to control actuation of the brake by a second brake control signalwhich is characterized by an automatic brake circuit which includes:

a deceleration comparator to receive the electrical signal from thewheel speed detector means, differentiate that signal, and compare thedifferentiated signal to a preset reference to produce a digitalelectrical error; and

a deceleration modulator to receive and integrate the digital electricalerror signal to producethe second brake control signal so as to supplyit to the means to control actuation of the brake. 6. A circuitaccording to claim 5 wherein the modulator includes an amplifiercombined with at least one resistor and a capacitor to form anintegrator, with the values of the resistors and the capacitorcontrolling the characteristic output of the integrator, and means tolimit the maximum output of the amplifier to prevent saturation thereof.7

7. A circuit according to claim 6 which includes gate means acting as aseries switch between the modulator and the means to control actuationof the brake, and means to externally control the gate means so as tosignal to the deceleration comparator so as to inhibit the output of thecomparator from being affected by other signals applied thereto andmeans to remove the predetermined DC signal upon application of theapply signal.

10. A circuit according to claim 6 which includes means to control theintegration rates of the modulator such that a negative rate ofintegration and positive rate of integration associated therewith areexclusively independent.

1. A brake control system for use on a moving vehicle having at leastone rotatable wheel, brake means for the wheel, means to represent wheelrotation as a voltage, and valve means responsive to an electricalsignal for controllably actuating the brake means, comprising: anintegrating amplifier for supplying the electrical signal to the valvemeans; a first circuit means supplying a static reference signal to theamplifier; a second circuit means responding to the means to representwheel rotation as a voltage and supplying a wheel deceleration signalrepresentative of the instantaneous rotation of the wheel to the firstcircuit means to produce the static reference signal therefrom forcontrol of the integrating amplifier and the valve means; skid detectorcircuit means supplying a signal indicative of skid conditions of thewheel to the valve to override the control output signal; and a firstlogic circuit which, in response to a first external command signal,controls the ability of the wheel deceleration signal to effect theoutput of the first circuit means.
 2. The brake control system accordingto claim 1 which further includes a second logic circuit, responsive tothe first external command signal, operative to supply the output of theintegrating amplifier to the valve means only when the first externalcommand signal is present.
 3. The brake control system according toclaim 2 wherein the first logic circuit, in response to a secondexternal command signal, controls the ability of the wheel decelerationsignal to affect the output of the first circuit means when the firstexternal command signal is present.
 4. The brake control systemaccording to claim 1 wherein the integration amplifier is such that theoutput thereof changes with respect to time at two separate and distinctrates depending upon the relative polarity between the static referencesignal and a predetermined reference.
 5. A brake control circuit for arotating wheel which comprises: a brake for the wheel; wheel speeddetector means to sense and indicate instantaneous wheel speed as anelectrical signal; a skid detector actuated by the electrical signalfrom the wheel spEed detector means so as to produce a first brakecontrol signal; and means to control actuation of the brake by a secondbrake control signal which is characterized by an automatic brakecircuit which includes: a deceleration comparator to receive theelectrical signal from the wheel speed detector means, differentiatethat signal, and compare the differentiated signal to a preset referenceto produce a digital electrical error; and a deceleration modulator toreceive and integrate the digital electrical error signal to produce thesecond brake control signal so as to supply it to the means to controlactuation of the brake.
 6. A circuit according to claim 5 wherein themodulator includes an amplifier combined with at least one resistor anda capacitor to form an integrator, with the values of the resistors andthe capacitor controlling the characteristic output of the integrator,and means to limit the maximum output of the amplifier to preventsaturation thereof.
 7. A circuit according to claim 6 which includesgate means acting as a series switch between the modulator and the meansto control actuation of the brake, and means to externally control thegate means so as to selectively control inclusion of the automatic brakecircuit into the brake control circuit.
 8. A circuit according to claim7 where the means to externally control the gate includes anapply-remove logic section which controls the operation of the gate inaccordance with an apply signal and further controls a modulator inaccordance with a remove signal coincident with the apply signal suchthat a smooth release of brake pressure may be achieved.
 9. A circuitaccording to claim 8 which includes means to continuously apply apredetermined DC signal to the deceleration comparator so as to inhibitthe output of the comparator from being affected by other signalsapplied thereto and means to remove the predetermined DC signal uponapplication of the apply signal.
 10. A circuit according to claim 6which includes means to control the integration rates of the modulatorsuch that a negative rate of integration and positive rate ofintegration associated therewith are exclusively independent.